This invention relates to mixing means (e.g., a disposable static-type mixer), a receptacle utilizing a static-type mixer of this invention and a method of packaging utilizing the receptacle and static-type mixer of this invention.
More particularly, the invention is concerned with packaging utilizing foamed-in-place plastic foam, such as a two-part polyurethane foam, which, in liquid form, is poured into a receptacle around an item to be packaged and then allowed to foam up around the item to form a shock-absorbing packaging material surrounding the item thereby to protect the article from damage during shipment. This packaging technique is broadly disclosed in U.S. Pat. No. 2,897,641 and has recently been adopted by industry and U.S. Government agencies to protect delicate instruments and other items.
Typically, polyurethane foams and other similar foam materials require that two chemical components be mixed in proper proportion immediately prior to their use, and that the mixture be immediately dispensed into the receptacle for foaming. These plastic foams often have a relatively short pot life (e.g., only a few seconds). Thus, the mixing and dispensing apparatus must be immediately cleaned after each use or the plastic foam material will set up and clog the apparatus.
Apparatus for mixing and dispensing two-part plastic foam mixtures is known which utilizes a motionless or static-type mixer for mixing the components. However, in this known apparatus, the static-type mixer must be immediately cleaned after each use to prevent clogging. According to U.S. Pat. No. 3,361,412 this is done by introduction of a flushing agent, such as methylene chloride solvent. In some types of mixing and dispensing apparatus, solvent flushing or purging is operator controlled. If the operator neglects to adequately flush the apparatus, the foam will set up this necessitating tear-down and clean-up of the apparatus. In more expensive mixing and dispensing apparatus, the solvent purge is performed automatically after each packaging operation. This flushing operation, whether done manually or automatically, requires time and consumes expensive solvent, thus slowing down production and increasing the cost of foamed-in-place plastic foam packaging.